TABLE OF CONTENTS
TABLE OF CONTENTS
LIST OF TABLES
LIST OF FIGURES
1.1 Background Information
1.2 Statement of the problem
1.3.1 Research Questions.
1.3.2 Research Hypothesis
1.5 Scope of study and limitation
1.5.1 Scope of Study
1.5.2 Limitation of the study
1.6 Assumptions of the study
2.2 Rivers and Pollution from Land Based Activities
2.3 Heavy metal and pollution
2.4 Sources of Heavy metal pollution
2.5 Heavy metals and water pollution
2.6 Heavy metals in Sediments
2.7 Heavy Metal pollution in Kenya
2.8 Kwale County and River Mukurumudzi
MATERIALS AND METHODS
3.2 Description of study area
3.3.1 Sampling procedure
3.3.2 Data collection approach
3.3.3 Data Collection Techniques
3.3.4 Validity and reliability of research instruments
3.3.5 Data Analysis and presentation
3.3.6 Validation of results
RESULTS AND DISCUSSION
4.1 Heavy metals in water
4.2 Heavy metals in sediments
4.3 Comparisons of heavy metals
4.3.1 Correlations between heavy metals
4.3.2 ANOVA Comparisons of heavy metal concentrations between sites
4.4 Water Contamination
4.5 Sediments Contamination
4.5.1 Geo-accumulation Index results
4.5.2 Contamination Factor (CF) results
CONCLUSIONS AND RECOMMENDATIONS
To my late dad Mr. Benson Mwashinga, my mum, aunt, friends and all who remembered me in prayer.
My sincere and deep felt gratitude are to, Pwani University for offering me the opportunity to do my Masters degree, specifically this goes to the School of Earth and Environmental Sciences. My supervisors, Dr. Loice Ojwang’ and Dr. Saeed Mwaguni for their tireless effort and dedication to ensure this work is thoroughly done. My Sponsor, The Kenya Coastal Development Project (KCDP) for funding my entire studies, you turned my dream to reality. Agriquest Laboratories, Mining and Geology Department, Rural Focus Kwale, Mark Melly, Oliver Ogolla, Kimega Ngala and Suleiman Mwakurya for every part you played in this research. May God bless you richly.
LIST OF TABLES
Table 1: AAS instrument operating conditions
Table 2: Percentage recovery for spiked pure metals through known standard addition
Table 3: Summary of Means±SD of Concentration of Heavy metals in water during Short rain, Dry and Long rain seasons
Table 4: Summary of Concentration Mean±SD of Heavy Metals in sediments during Short rains, Dry and Long rain season
Table 5: Pearson correlation and P-test values
Table 6: Guidelines of concentration of metals in water from WHO, NEMA and KEBS
Table 7: Pb I-geo values for sediments sampled along different points during different seasons
Table 8: Fe I-geo values for sediments sampled along different points during different seasons
Table 9: Cu I-geo values for sediments sampled along different points during Long rain
Table 10: Metal Contamination Factors (CF) for sediments of all sites studied in River Mukurumudzi for all the seasons
LIST OF FIGURES
Figure 1: A simple sequence for the analysis of water for heavy metals using an AAS
Figure 2: a) Sample collection b) An operational dam along the course of the river c) People swimming in the river at Bomani Village. d) A resident of Shimba hills fetching water for use from the river
Figure 3: Comparison of heavy metals in water and sediments
Figure 4: Comparison of metals between water and sediments across sampling points
LIST OF ABBREVIATIONS AND UNITS
Abbildung in dieser leseprobe nicht enthalten
Rivers are the major sources of water being used in cities and its environs. This water may either be treated or untreated. River banks could be very busy, varied activities ranging from farming to industrial activities and other domestic household activities are conducted. The present study aimed at investigating the potential sources of selected heavy metal contaminants in River Mukurumudzi, Kwale County. Water and sediments were sampled in four points along the river impacted by mining, human settlements and agricultural activities for three different seasons. The samples were analyzed for Iron, Lead, Cadmium, Copper and Arsenic using an AAS. Sediment quality was also analysed by the calculation of CF and I-geo values. Interpretation of results was conducted using Minitab statistical software and Excel spreadsheets. The range of metals in water during the dry season was Fe (0.19-0.32) mg/l, Pb, Cu, Cd and As were below the detection limits. The range of metals in water during the short rain was Fe (0.12-1.25) mg/l and BDL for all other analysed metals. The range of metals in water during the long rain season was Fe (0.07-1.82) mg/l, Cu (0.08-0.11) mg/l and BDL for all the other analysed metals. The range of metals in sediments during dry season was Fe (0.13-1.44) ppm, Pb (0.08-0.54) ppm, and BDL for all other analysed metals. The range of metals in sediments during short rain season was Fe (0.23-1.73) ppm, Pb (0.12-0.27) ppm, and BDL for all other analysed metals. The range of metals in sediments during the long rain season was Fe (0.25-2.75) ppm, Pb (0.09-0.34) ppm, Cu (0.10-0.14) ppm, and BDL for all other analysed metals. The CF values for sediments were all <1 which indicated low contamination. The I-geo values of metals in sediments were all <1 suggesting the sediments are practically unpolluted. The concentrations of metals in water were all within the NEMA, KEBS and WHO limits thereby indicating non-contamination. River Mukurumdzi water and sediments are not contaminated by heavy metals. However, there is need for the land based activities to be assessed since elevation of metal concentration was observed during the rainy seasons because of run-off from these sources.
KEY WORDS: Heavy metals, AAS, BDL, Sediments and Water contamination, I-geo and CF.
1.1 Background Information.
Water is essential for life. It is utilized for domestic purposes, agricultural production, industrial activities, and among many other uses. Water is a basic amenity to humanity on the planet earth. Water is managed poorly in many parts of the world despite it being important for life (Fakayode, 2005). Water is a good solvent; and due to this characteristic, water will always dissolve and contain mineral constituents and other substances that it leaches out on contact. Naturally, pure water is hard to find. The contamination of water in a particular area is always directly related to the degree of contamination of its environment (Peng et al., 2005). While trickling down rainwater collects impurities from the atmosphere. Consequently, impurities from surface run-off, sewage discharges and industrial effluents are collected by rivers and streams in their course of flow (Skeat, 1969). Rivers and streams are important sources and channels for the movement and transportation of anthropogenic metals to the ocean (Everaats and Niewenhuize, 1995; Nicolas et al., 2006; Adamo et al., 2005).Water pollution from anthropogenic activities has been documented in many parts of the world (Adenkule, 2009; Lars,2003). Many rivers, lakes, wetlands, ground waters and oceans suffer a great loss of degradation from various human activities. These activities have effects on water quality, changing both its physiochemical and biological parameters making it unsuitable not only for domestic use, but also for other purposes. Water pollution also has effects on habitats, causing species migration for species that cannot adopt, while exterminating others due to impacts that affect their reproductive abilities. There are many sources of water pollution but the main ones are pollution from industrial and municipal waste-water discharges, inputs from agricultural activities that include the use of fertilizers and chemicals, seepage from waste sites, decaying plant life, road, railway and sea accidents involving large oil tankers etc., all leading to environmental degradation, and the necessity for environmental protection. (Kinchella and Hyland, 1993).
New challenges in environmental protection and conservation that have resulted due to global changes bring the need for baseline data to evaluate the potential impact of pollutants to ecosystems (Amune et al., 2012).
Heavy metals in the environment lack natural elimination processes. As such, heavy metals occur naturally in the earth’s crust at varying concentrations in all ecosystems. Unfortunately, human activities have drastically interfered with the biogeochemical cycle and balance of heavy metals in the various ecosystems (Joseph et al., 2012).Environmental pollution became extensive as mining, industrial activities and mechanized agriculture activities increased in the 19th century and have intensified since then (Torres et al., 2012). Pollution of ecosystems such as rivers, oceans, lakes and wetlands by heavy metals resulting from anthropogenic impact is causing serious ecological problems in many parts of the world. This is exacerbated by the lack of natural elimination processes for heavy metals in the environment.
In the past microbial quality of water for potable uses was of concern and was often given the first priority due to the immediate and potential devastating consequences of waterborne infectious diseases (Schmoll et al., 2006). Currently however, increased concern has shifted over to that the concentration of heavy metals in water because the public has now become aware of the toxic effects of heavy metals on human health. In that case, globally heavy metal pollution has been marked as a serious environmental problem owing to their persistent and accumulative properties (Yuan et al., 2004; Okuku,2007)
Heavy metals are persistent in the environment and they tend to shift from one compartment of the ecosystem to another. In the aquatic environment these metals shift from water to the sediments and then the biota. Some of the heavy metals like iron, copper, cobalt, zinc, manganese and chromium(III) are essential metals since they are required by the body to perform physiological functions of living tissue and regulate many biochemical processes ( Ismail et al,. 2001).
Non-essential metals are those metals that are not required by living systems and can be toxic even in trace amounts, these include: cadmium, mercury, lead, titanium, arsenic, bismuth and antimony (Tyagi and Mehra, 1992). Whether essential or non-essential, all metals are toxic at higher concentrations with their toxicity linked to chronic diseases such as renal failure, liver cirrhosis, brain syndrome, itai-itai and many others (Salem et al., 2000). These metals continue to pile in concentration to higher levels when they are discharged into natural waters at increased concentrations from agricultural, industrial and domestic wastes, pesticides or mining operations. As a result, they end up having severe toxicological effects on humans and the aquatic ecosystem.
Trace amount of metals are naturally present in freshwaters from weathering of rocks and soils. However, anthropogenic activities like mining release huge amounts of tailing waste containing heavy metals which could pose serious threat to water sources, agricultural soils and food crops ( Jung,2001; Ezeh and Chukwu, 2012). Heavy metals may be introduced and spread in the environment through combustion, extraction, agricultural runoff and transportation (Lars, 2003).
Agrochemicals introduced in the soil as soil nutrients to improve fertility contain metals which in most cases exceed the limits set for land application and their continuous use can exacerbate their accumulation in agricultural soils (Lim et al,. 2008; Hesterberg, 1998). The use of agrochemicals such as pesticides and fertilizers may result in undesirable accumulation of trace elements like Cd, Cu, Pb and Zn (Merwin et al., 1994).
The use of composts and bio solids has been shown to increase cadmium, copper and zinc in soils while phosphate containing fertilizers have been found to enhance leaching of cadmium from soil (He et al., 2005). Copper oxides, chlorides, sulfates, ethanoates, bromides and carbonates are widely used in pest control, inorganic dyes as fungicides, seed disinfectants and algaecides. Potassium permanganate is used domestically as an oxidant for disinfection, bleaching and cleaning. Zinc is used for galvanizing steel and iron products and zinc carbamates are used as pesticides (Mohammad and Shashi, 2006)..
Heavy metals are also common in industrial applications such as their use in manufacture of pesticides, fungicides, batteries, alloys, electroplated metal parts, textiles, pigments, dyes, and steel industries (Mohammad and Shashi, 2006). Other uses of heavy metals include; industrial use in pharmaceuticals, cosmetic, dental amalgam and paints manufacturing.
The Kenyan coast is endowed with a wide variety of natural resources. However, it is acknowledged that the region is water deficient. This deficiency is informed by the poor geographical distribution of the commodity rendering some areas to resort to water resources that are unsuitable for domestic purposes without purification measures. As a result of surface water sources yielding inadequate supplies of freshwater, the majority of households have opted to rely on groundwater as alternative source of freshwater for potable purposes. As if this is not enough, natural resources, including water have suffered degradation over the years compromising opportunities for livelihood (Munga et al., 2006). The scarcity of the water resources notwithstanding, many of the freshwater sources such as springs, aquifers, rivers and many others are either threatened by degradation of the environment or face the threat of pollution from population pressures. It is this concern that led the study on the water resource, making it paramount to understand its status as a safeguard for all freshwater sources not currently impacted and the desire for conserving them for sustainable development (Adegbola and Adewoye, 2012; Olajire and Imeokparia, 2000).
The water situation, is as was described: scarce in the country, yet future projections show as a result of population growth, the per capita available water currently at 650m3/year, will likely drop to 359m3/year by 2020 (Marshall, 2011). This figure is far much below the global accepted value of 1000m3 year-1 per capita level. Therefore, the capacity of the water sector has to be improved for the provision of clean and safe drinking water (GoK, 2007).
A majority of Kenyans particularly those in the rural areas have limited access to quality water. Many of them walk long distances in search of water and use it untreated and raw from lakes, rivers and dams. The untreated water is not only turbid, but could also be laden with disease causing bacteria and in some cases, chemicals. The problem is further exacerbated by the seasonal fluctuations of water availability which is more correlated to the seasonal distribution of rainfall in most parts of the country (Kithiia, 2014). In addition, agricultural chemicals (fertilizers and herbicides), urban and industrial wastes, as well as use for hydroelectric power puts water resources in Kenya under pressure. Thus, increase in demand for water resources causes many constraints and leads to the pollution of the available water resources. Water pollution from urban and industrial wastes, comprises another environmental problem.
Kenya has 20.2 cubic kilometers of renewable water resources with 76% being used in farming activity and 4% used for industrial purposes. Only about 42% of the residents in rural areas and 88% of city dwellers have pure drinking water (Marshall, 2011). The impact of pollution on water resources is manifested by water of poor quality which gives rise to water toxicity to mammals and aquatic life; loss of aesthetic value by becoming unsuitable for recreational activities, high cost of water supply as polluted water is expensive to treat, eutrophication, de-oxygenation, acid rain and habitat modification (Kithiia, 2014).
The Kwale County is endowed with a wide variety of mineral ores masking the area potential for mining activities. Mining operations disturb the ground with ores formally trapped underground becoming disrupted and scattered hence finding their way onto the human environment where they accumulate owing their persistency, leading to environmental pollution. Heavy metals which may be part of the disturbed ore may be environmentally stable and hence toxic to plants and animals at higher concentrations. These metals tend to accumulate in the tissues of plants and animals causing chronic adverse effects like chronic lung disease, emphysema, kidney disease, arthritis and cancer among others. These metals contaminate water thus limiting its beneficial use for domestic and industrial application (Petrus and Warchol, 2005). River Mukurumudzi could be suffering from the effects of mineral discharges into its waters (Katuva, 2014), hence the motivation for this study.
The Mukurumudzi River basin (MRB) covers an area of 207 Km² and is located in the Kwale County approximately 50 Km south of Mombasa. It starts 30 Km inland of the Indian Ocean. The basin has the Mukurumudzi River, 40 Km long as the main river flowing from Shimba hills and draining into the Indian Ocean (Osoro, 2011). The catchment houses two major industries- a titanium mining company and an irrigation farm. The mining is being undertaken by the Base Resources Mining Company while irrigation of 8000 ha of sugarcane is being done by the Kwale International Sugar Company (KISCOL). Both the mining and irrigation companies have so far developed 3 dams on the Mukurumudzi River to meet their water needs (Katuva, 2014).
The river flows out of the Shimba hills National Reserve where a water pumping project by Majimboni Self Help Group has been set. Water is pumped from the river by a generator, after which, it is supplied to various households in the area. The river then follows through the Shimba hills town, before entering the Base Titanium mining company which has dammed the same for supplying its daily water needs for the mining activity. The company uses approximately 2000 cubic meters of water daily and the dam created has a capacity for abstracting 8.4 million cubic meters of water. The water in the dam is supplemented by the Gongoni borehole during low river flow in the dry seasons. Midway the river is a community on settlement scheme, where the local people who abstract water from the river for small scale farming activities and for other domestic purposes, such as bathing in the river, and washing of clothes (Katuva, 2014).
The River is also dammed further downstream by the Kwale International Sugar Company (KISCOL) for its irrigation activities for sugarcane plantations. The KISCOL has created two dams for its activities, the upper Koromojo and lower Koromojo dam. These activities carried alongside the course of the river form the basis for this study since the potential release of heavy metals, is going to be assessed, with the activities carried out, being potential sources of the contaminants (Katuva, 2014; Kayumba, 2014).
Among other activities, River Mukurumudzi supports farming, fishing, domestic and recreational activities of the local communities around it. Any dilapidation of this river through pollution will have very crucial negative impact in the livelihoods of local communities. In many instances, increasing water demand and use always results to contamination and deterioration of its quality.
The waters of River Mukurumudzi could be contaminated by heavy metals from the mining activities, agricultural and domestic activities that are all carried along the river. Fertilizer in farming and residual fertilizer in soil as noted by Adenkule (2009) can leach through soil along with rainwater and hence being a source of heavy metals to the river. The discharge of grey water from washing basins and bathing in rivers where soap has been used is another potential source of heavy metal contamination.
1.2 Statement of the problem
The Kwale District Assessment Environmental Report (1985), states that Kwale district is endowed with a variety of mineral ores such as iron, limestone, zinc, zircon, gypsum, manganese, lead, niobium, titanium, molybdenum, nepheline and gorceite. This shows that any disturbance of the ground has the potential to expose these ores to the action of air and water erosion to cause them find their way into the human environment. Therefore, there is a high possibility for the heavy metals present in the ores to enter and accumulate in the soil and waters of the region through runoffs, seepages and leaching operations, rendering the water unfit for human use, in an otherwise, water scarce area –an occurrence that calls for water conservation.
This study undertakes to elaborate on the land based activities undertaken along the course of River Mukurumudzi to determine the potential levels of heavy metal contamination that could occur as a result of the land based activities along the river. This focus of the study is therefore the determination of the levels of some selected heavy metals in water and sediments of this river.
The main objective of this study is to assess the level of heavy metals in the Mukurumudzi River with respect to contamination from potential anthropogenic sources that include mining and farming activities through the following specific objectives:
i. Determine the level of the heavy metals Pb, Fe, Cu, Cd and As in the waters of River Mukurumudzi around the Shimba hills area, Base Titanium Plant (BTP) area, KISCOL plantations and Bomani village during short rains, heavy rains and dry seasons.
ii. Determine the level of the heavy metals Pb, Fe, Cu, Cd and As in the sediments of River Mukurumudzi around the Shimba hills area, Base Titanium Plant (BTP) area, KISCOL plantations and Bomani village during short rains, heavy rains and dry seasons.
iii. Compare these values with their natural occurrence in freshwater bodies.
iv. Using contamination indices to assess the degree of contamination in sediments of River Mukurumudzi.
1.3.1 Research Questions.
In order to achieve the set objectives the study sought to answer the following research questions:
i. What are the concentrations of heavy metals (Pb, Fe, Cu, Cd and As) during the long rains, short rains and dry season in both surface waters and in the sediments of the river at Shimba hills area?
ii. What are the concentrations of heavy metals (Pb, Fe, Cu, Cd and As) during the long rains, short rains and dry season in the surface waters and sediments of the river in the other 3 points which are impacted by anthropogenic activities?
iii. Are the levels of heavy metals in the river comparable to their natural occurrence values in freshwater bodies?
iv. What are the Contamination Factor and Geo-accumulation values of the metals in sediments?
1.3.2 Research Hypothesis
H0: There is no relationship between heavy metal contamination in the river and the anthropogenic activities taking place in its basin.
H1: There is a relationship between heavy metal contamination in the river and the anthropogenic activities taking place in its basin.
Water pollution and quality degradation is a growing problem, exacerbated by the growing anthropogenic activities in developing countries. It is becoming a threat to the existing natural water resources functions and uses. This is attributed to the increasing quest of industrialization and exploration of resources and diversification of national development goals, experienced globally, with Kenya not being an exception (Kithiia et al., 2011).
The justification for this study is that the pollution of water resources is one of the major causes of the scarcity of freshwater in the Kenyan coast necessitating the need for conservation of freshwater sources and supplies. Heavy metal pollution poses danger to the life of humans and organisms. Heavy metal pollution affects the availability of freshwater sources for domestic use (Okoth and Otieno, 2000). Communities living in Nguluku( within the study area) do not have access to tap water but draw water from boreholes, wells and surface sources in form of the river traversing the area. Out of the total of the area, 42% get water from boreholes, 42% from wells, 13% from streams and 3% from the river (Kayumba, 2014). Out of the 3%, a majority draws water upstream and away from major human activities since the river water is in good condition. As the river moves downstream, many activities are carried out along its course, affecting the quality of the water, forcing many people to resort to other sources of water for its potable needs.
A study conducted by Maina (2008) reported high concentrations of heavy metals in the soil of the area. This formed a justification to study heavy metal concentration in the sediments to establish how land based activities influence the distribution of these metals in the river bed.
The data obtained from this research will form a baseline for other studies that may be carried in this area in future.
1.5 Scope of study and limitation.
1.5.1 Scope of Study
The study focused only on five metals (Pb, Fe, Cu, Cd and As). These heavy metals were considered prevalent in the area, as informed from literature survey. The study also focused itself on River Mukurumudzi since a lot of studies haven’t been done in this river, proof of its importance in the area.
1.5.2 Limitation of the study
The following were the limitation to this study:
i) Hindrance caused by accessibility of the entire river course due to limitation imposed by the terrain of the river;
ii) Hindered access due to safety concerns caused by the presence of crocodiles and other wildlife in the river basin;
iii) Unavailability of previous data of the contamination status of the river.
1.6 Assumptions of the study.
In this study, the following assumptions were made:
i) The heavy metal concentration of a particular site was reflective of the contribution of the land based activities taking place around that particular area;
ii) The heavy metal concentration levels were attributed only to the activities taking place along that particular sampling point.
This chapter provides key information on rivers and pollution from land based activities, it explains heavy metal pollution in the global, regional, national and local perspective and it also identifies gaps in literature.
2.2 Rivers and Pollution from Land Based Activities.
Aquatic ecosystems such as rivers, dams and lakes are sources of livelihood to many rural communities in Africa. However, in the recent past, they have been subjected to various forms of degradation due to pollution arising from domestic wastes, industrial effluent, agricultural run offs and bad fishing practices (Ndimele, 2008).
Many studies have indicated that surface waters are majorly polluted by land based activities as compared to ground water. Rivers are conduits and channels for the transportation and movement of water to the ocean. Rivers tend to collect impurities and other materials as they move as a result of activities that occur and are conducted along their course of flow, this may reduce the capacity of the river and also the availability of its waters for various uses as it travels downstream. The bulk of the pollutants come from activities related to man though natural sources also play part. It has been studied that the intensity of land uses and activities that are carried alongside a river’s channel is directly related to the pollution status of that river, this is explained that the amount of waste discharged tends to increase with increasing water demand.
Studies by Kithiia (1992, 2006), Okoth and Otieno (2000) and Mavuti (2003) reveal degradation trends in water quality within the river system due to changes and intensity in land use activities.
2.3 Heavy metal and pollution
The contamination of ground, stream and river water ecosystem by heavy metals is a worldwide environmental problem. The public has become more concern over the potential accumulation of heavy metals in various ecosystems (Wong et al., 2002). Global chemical pollution has been a great concern with the increase awareness of the public towards environmental issues (Mathiranan et al., 2005).
Pollution of ground water and surface water systems is a major environmental issue throughout the globe (Hutchison et al., 1993: WHO, 1998). Land based activities have a major impact on natural resources including water, soil and plants. Heavy metals in rivers are contributed by both natural and anthropogenic sources. Heavy metals have been accumulating for years in sediments, water and biota of lakes and streams, (Fakayode, 2005) stated that heavy metals may heavy effects on the ecosystem as greater than those of more common pollutants. Heavy metals and their salts are also found in industrial wastes and agricultural runoffs.
Heavy metals always gain access into the river systems from both natural and anthropogenic sources and these get distributed in water and sediments in the course of their transportation. The spatial distribution and the temporal behavior of metals is essential information for environmental research (Marvin et al., 2002; Obiajunwa et al., 2002).
Copper concentrations as low as 1-2 µg/L have been shown to have adverse effects on aquatic organisms. Copper can affect the reproduction, physiology and behavior on a variety of aquatic organisms. Moreover, high intakes of copper have been associated with liver failure and gastrointestinal problems in humans (WHO, 1998,Förstner and Wittmann, 2012).
Iron is one of the most abundant elements in the world. It is found in a number of minerals, rocks, sediment and soil. It is an essential mineral to all organisms. However, iron has been associated with acute poisoning in young children (30lb) who took 5-9 iron supplement tablets of 30 mg each. Iron is absorbed rapidly once ingested and becomes corrosive. Iron poisoning targets organs like liver, kidneys and cardiovascular system (Baby et al., 2010).
2.4 Sources of Heavy metal pollution
Heavy metals always gain access into river systems from both natural and anthropogenic sources, these get distributed to sediments and biota as they move from one level to another. An area that naturally contains mineralized rocks usually contains an elevated level of metals, the trace metal level of river water is always controlled by the abundance of metals in rocks of the river’s catchment area and their mobility (Olajire and Imeokparia, 2000).
Natural sources are, soil erosion, primarily rock weathering and dissolution of water soluble salts. Naturally occurring metals always move through aquatic environments usually without detrimental effects. They move independently of human activities (Garbarino et al., 1995). Degrading environmental conditions and growing reliance on agrochemicals have led to an increasing public concern over the potential accumulation of heavy metals and other contaminants in agricultural soils (Nriagu, 1988; Alloway, 1990; Pendias, 1995).
Heavy metals are released to a river from various sources, they enter the ecological systems through anthropogenic activities such as sewage sludge disposal, organic fertilizer and pesticide application and also through atmospheric deposition (Haiyan and Stuanes, 2003). Anthropogenic activities like mining, ultimate disposal of treated and untreated waste effluents containing toxic metals as well as metal chelates from different industries (Amman, et al.,2002) and also the use of heavy metal containing fertilizers and pesticides in agriculture indiscriminately resulted in deterioration of water quality rendering serious environmental problems posing threat on human beings (Lantzy and Mackenzie, 1979; Nriagu, 1979;Ross, 1994) and sustaining aquatic biodiversity (Ghoshand Vass, 1997; Das, et al., 1997)
Some fertilizers and pesticides are known to contain various levels of heavy metals including Cd and Cu (Kabata-Pendias, 1992). There is therefore a possibility that the continuous and heavy application of agrochemicals and other soil amendments can potentially exacerbate the accumulation of heavy metals in agricultural soils over time (Siamwalla, 1996; Chen et al., 1999).
Copper is the active ingredient in some pesticides applied to agricultural crops to inhibit fungal growth (Mcneely et al., 1998). Copper is generally present in only trace levels in natural surface waters up to a concentration of 0.005 mg/l and higher levels are usually associated with anthropogenic sources (Mcneely et al., 1998). Ground and surface water is threatened by the excessive use of fertilizer and pesticides in agricultural activities (Hariprasad and Dayananda, 2013). Agricultural runoff containing heavy metals reaches natural water bodies affecting aquatic species and in turn ecosystems (Hariprasad and Dayananda, 2013). Heavy metal contamination of soil in agricultural areas is linked to the use of fertilizers, pesticides and herbicides by farmers (Mingorance et al., 2007; Yang et al., 2005; Dankoul et al., 2012). The use of agrochemicals such as pesticides and fertilizers may have resulted in undesirable accumulation of trace elements such as arsenic, cadmium, copper, lead and zinc in soil (Merwin et al., 1994; Van Gaans et al., 1995; Harris et al., 2000).
Metal mining activities release huge amounts of tailing and waste containing heavy metals which pose a serious threat to water sources and the environment (Jung 2001; Ezeh and Chukwu, 2012). Heavy metals can also be introduced into soils from various sources, including atmospheric deposition of metal/ metalloids bearing particles.
2.5 Heavy metals and water pollution
Water pollution is a major threat to human population and dumping of pollutants into water body resulted in rapid deterioration of water quality and affect the ecological balance in the long run. Pollution refers to any direct or indirect alteration of physical, thermal, biological or chemical property of water or water source so as to make it less fit for any beneficial purpose for which it is expected to be used or make it harmful or potentially harmful to the welfare, health or safety of human beings, any aquatic or non-aquatic life and property or the environment (Goel, 2000: Kinchella and Hyland, 1993).
Water pollution has been suggested to be the leading worldwide cause of deaths and diseases (Pink, 2006) and it accounts for the deaths of more than 140,000 people daily (West, 2006). Current concerns in environmental protection are majorly focused on water due to its importance in maintaining human health and ecosystem health (Mahananda et al., 2010).
Water will always contain minerals and organisms that it collects from materials it comes into contact with due to its chemical properties. Depending on the type and the concentration, these constituents may be toxic and therefore harmful to human beings (Elinge et al., 2011).
Recently however, increased concern over the concentration of heavy metals in water has developed as the public becomes more aware of their toxicity and impact on human health. Many metals occurring in nature are not harmful at trace concentrations and some such as iron, copper, cobalt, Manganese, Zinc and Chromium are even essential for proper functioning of the human body (Ismail et al., 2011; Amartey et al., 2011). All metals however are toxic at higher concentrations, with their toxicity being linked to chronic diseases such as renal failure, liver cirrhosis, hair loss and chronic anemia ( Salem et al; 2000). Heavy metal pollution has received huge worldwide concern owing to its persistence, toxicity, accumulation in the ecological system and risk to human health (Chang, 2003; Varol and Sen, 2012).
Heavy metals find their way to the waters through underground seepage of effluents arising from human activities, runoff from farms and industries, leaching and dissolution of metals occurring naturally in rock and soil. However, water pollution has been focusing on other aspects of water with a minimal interest in heavy metals. Heavy metal pollution has usually been relegated. It has only been brought to the fore if contamination due to anthropogenic sources such as poor waste disposal is suspected. In this respect, heavy metal content in water is given little attention in many rural areas due to fewer sources of pollution. This notwithstanding, heavy metal contamination of water in rural areas is still possible arising from obscure sources, fertilizers and the existence of mineral resources (Adegbola and Adewoye, 2012).
Among the inorganic contaminants of the river water, heavy metals are getting importance for their persistent nature and often accumulate through tropic levels causing a deleterious biological effect (Jain, 1978). Heavy metals exposure to human beings has been associated with development retardation, kidney damage, various forms of cancer and in some instances death.
2.6 Heavy metals in Sediments
Contamination of sediments by heavy metals and other pollutants is considered by many regulatory agencies to be one of the major threats to aquatic ecosystems. The importance of sediments as a sink for a range of substances including nutrients, hydrocarbons, pesticides and heavy metals has been highlighted in many past studies (Baldwin and Howitt, 2007).
Sediments are indicators of environmental contamination of water bodies by heavy metals and toxic compounds. Sediments act as sink for pollutants hence their monitoring is important for tracing the spreading and impact of pollution related changes; sediments accumulate heavy metals from the surrounding geogenic and anthropogenic sources (Acero et al., 2003; Casas et al., 2003; Pekey, 2006). In a river, bed sands perform a container and carrier for settlement and conveying of heavy metals and heavy metal is a persistent pollutant (Gibbs, 1973; Luoma et al., 1981; Bettinetti et al., 2003; Hollert et al., 2003; Jiang et al., 2010). Sediments are sinks of heavy metals in aquatic environments (Monteiro et al., 2012). When favorable conditions occur, the heavy metals settled in the sediments could gradually be released in the water and this phenomenon is one of the critical problems facing aquatic environments. Given their toxicity and bio-accumulation, many studies have shown that high heavy metal content in sediments could impact significantly the health of aquatic ecosystems (Suresh et al., 2011; Keskin and Toptas, 2012).
Heavy metals in sediments are not permanently fixed, and can be released back to the water in case of changes in environmental conditions like pH, redox potential, and among others. This is because sediment act as carriers of the heavy metals in aquatic ecosystems (Horstall et al., 1999;Forstner, 1981).
Many studies have found that sediments in aquatic ecosystems habour persistent and toxic chemicals more than the water column (Casper et al., 2004; Linnik and Zubenko, 2000). Monitoring of sediments is therefore very important in tracing the spreading and impact of pollution related changes.
2.7 Heavy Metal pollution in Kenya.
In Kenya heavy metal pollution monitoring is a prime area of research since the concentration of heavy metals in aquatic ecosystems affect the fish industry which is a major source of livelihood (Ochieng et al., 2008).Kenya faces serious problems of urbanization, vehicular pollution and industrial discharges that present serious health risks and exposure to the public (Abuor, 2011). In Kenya; Nairobi, Mombasa and Kisumu are the most industrialized and populated towns, elevated levels of heavy metals have been reported in the soils of these cities (Onyari et al., 1991; Kamau, 2001; Makokha et al., 2008). Studies on heavy metal contamination have been conducted in Lake Victoria (Oyoo-Okoth et al., 2010), Winam Gulf and Rift Valley lakes (Ochieng et al., 2007), Lake Naivasha (Kamau et al., 2007), Port-reitz creek (Kamau, 2001). Most of these studies have reported the presence of heavy metal contamination in these aquatic ecosystems. However, fewer such studies have been conducted on rivers which are the main channels of water and suspended matter to the oceans and also lakes. The presence of heavy metals in rivers as a result of their use in modern society is a matter of ever-growing concern to politicians, authorities and the public in Kenya (Kosgey et al., 2015). Oyoo-Okoth (2010) conducted a study of heavy metal pollution in Lake Victoria and found out that the concentration of Pb and Cu in water reflected anthropogenic pathways. In another study conducted by Abuor (2011) on the levels of heavy metals in scalp hair of people living in different places in Kenya, people from Msambweni District exhibited a high concentration of Pb and Cu.
2.8 Kwale County and River Mukurumudzi
Like many coastal regions, the richness of mineral resources is observed in Kwale County. There are also deposits of rare earth elements such as niobium and titanium (Ministry of Environment and Natural resources, 1985). Kwale County is a mineral loaded area, these minerals include Titanium(Rutile, Ilmenite and Zircon) at Nguluku Shimba hills, Gemstones at Kuranza, Rare Earth Elements (Niobium, Phosphates) at Mrima hills and Samburu, Silica sand at Waa, Tiwi and Ramisi, Zinc, Lead and Copper at Mkang’ombe, Mwache Dumbule and Dzitienge, Sandstone at Mariakani, Limestone at Shimoni and Waa among others(County Integrated Development Plan, 2013).This has led many mining companies to camp at the area to conduct various mining and prospective activities. The exploitation of these minerals has faced consistent opposition from environmentalists because of the adverse impacts that might result from it. The county however lacks basic amenities such as piped waters and therefore residents are forced to rely mainly on groundwater from hand-dug wells and other natural water sources for domestic use (Chege et al., 2013). The Kwale County Integrated Development Plan of 2013 states that the average distance to the nearest water point in the county is 2Km, this is well above the internationally required 5M distance to the nearest water source. The plan also states that the lack of clean water in the County increases the occurrences of water-borne diseases and illnesses among the local population. Mukurumudzi River being one of the natural water sources available in the area is a major source of fresh water to the communities around (Katuva, 2014). River Mukurumudzi is the largest river in Kwale County in terms of volume, carrying approximately 9917M³/D ( Kwale County Intergrated Development Plan, 2013).
The resource development and change of hydrological regime, sediment and water quality in the Mukurumudzi River has attracted great attention (Katuva, 2014). There are a lot of abstraction points along the river that brings about diminishing water availability. The major abstractors are KISCOL and Kwale Mineral Sands Project (WRMA and WRUA, 2012). As a result of over abstraction and diminishing water resource, environmental water flow requirements are compromised leading to environmental degradation (Tennant, 1976; Reiser et al., 1989). The key threats to water in Kwale are water scarcity, pollution and quality (Mutua, Thomas and Hope, 2015).
Previously done studies have tended to concentrate on the levels of heavy metals and radioactivity contamination in soils and groundwater in the area. However, no such study has been conducted on the concentration levels of heavy metals in River Mukurumudzi. This study therefore tends to come up with baseline information on the levels of heavy metals in this river and also analyze its current status with regards to heavy metal pollution (Maina, 2008; Osoro, 2011; WRMA and WRUA, 2012).
MATERIALS AND METHODS
This chapter provides a description of the study area of the sampling location, sampling methods, methods of sample analysis and data analysis.
3.2 Description of study area
The study area lies within the area bounded by the longitudes 40 16’ 30” S and 40 25’ 30” S and latitude of 390 22’ 30” E and 390 31’ 30” E. The geology of the area is characterized mainly by coral limestone of Pleistocene age and Magarini sands. The Magarini sands consist of unconsolidated sediments derived from the Duruma sandstone series that were deposited during the tertiary ages. The region has a typically high water table making groundwater accessibility relatively easy.
The region is composed of Nguluku, Maumba and Shimba villages and the estimated population of is approximately 6,000 people.
The land within the catchment is mainly used for; Subsistence farming of crops including maize, beans, cowpeas, millet and sorghum, okra, cassava; commercial mining; commercial farming of sugarcane; livestock husbandry (cattle, sheep, goats etc); tourism associated with the sea and Shimba Hills National Reserve and fishing mainly in the Indian ocean. The main economic activities in the catchment include; subsistence farming; livestock keeping; commercial fishing; sand harvesting; commercial farming of sugarcane and commercial mining.
The Mukurumudzi River basin lies astride the boundary between the coastal plain underlain by Pleistocene corals and sands and a line of low lying hills underlain by Pliocene sands. To the West, the Shimba Hills are underlain by faulted and moderately folded sandstones of Triassic age, the Mazeras sandstones. The groundwater flow in the study area is driven by gravity head from the West, either from the Pliocene sand dunes or from the Shimba Hills to their west/north west (Caswell, 1953).
The Mukurumudzi River basin covers an area of approximately 230 km2 and is located in Kenya, approximately 50 km south of Mombasa (Kenya‘s principal port facility), and starts 30 km inland from the Indian Ocean. The Mukurumudzi River basin has the Mukurumudzi River, 40 km long, as the main river flowing from the Shimba Hills and draining into the Indian Ocean.
This river basin experiences a sub-humid climate, with 1100 mm to 1300 mm of rainfall (1959 to 2012) split between the long (April-July) and short (August -October) rains respectively.
3.3.1 Sampling procedure
Randomly selected different points along the river where pollution sources are evident were identified based on their proximity to pollution sources. Three sampling areas were selected. One adjacent to the Titanium mining company(4°25’9”S,39°26’35”E), the second one adjacent to human settlements at Bomani village (4°27’24”S, 39°28’51”E), and the third one adjacent to the KISCOL plantations (4°26’46”, 39°29’12”). A fourth sampling area was selected upstream near the source of the river where a lot of anthropogenic activities do not take place.
Sampling of both water and sediments was carried out twice for each of the three different seasons; during the short rains (August -October), during the dry season (January-March) and during long rains (April-July).
During each sampling time, three samples of water and three samples of sediments were collected for all the four sampling points. A total of 24 samples were collected at each time of sampling.
220.127.116.11 Water sampling and Aqua-regia oxidation.
Water was sampled at the four points located along the river. The water was sampled in triplicate and was contained in 500ml polyethylene bottles twice seasonally for the three seasons. This brought a total of 24 water samples per season. The samples were then preserved by adding 5ml nitric acid to each sample.